Potential Energy and Kinetic Energy

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Energy exists in many different forms, such as mechanical, thermal, chemical, gravitational, nuclear, kinetic and potential. The two forms of energy that are of special interest in physics are potential energy and kinetic energy. From the smallest of particles to the largest of stars, these two forms of energy exist everywhere in the universe.

What is potential energy?

Potential energy is the energy possessed by an object due to its position relative to other nearby objects. Examples include a boulder sitting at the edge of a cliff above a beach and a stretched catapult with a pebble in it. Work is done when potential energy is converted into kinetic energy. If the rock falls, it can do massive damage to the beach. If the spring is released, it can send the pebble flying off at a high speed.

There are several different types of potential energy:

  • Elastic potential energy: This is the potential energy stored in a stretched or compressed elastic object. The more the object is stretched or compressed, the more potential energy it has. Mathematically, it is expressed by the equation PEspring = x, where k is the spring constant and x is the amount of compression.
  • Gravitational potential energy: This is the potential energy stored in an object suspended at a height above the ground. The amount of energy stored in the object depends on its height and mass. It is captured in a formula as PEgrav = m.g.h, where m is mass, g is acceleration due to gravity and h is the height of the object.
  • Magnetic potential energy: This is the potential energy stored in magnets and magnetic objects. The nearer they are to each other, the higher the amount of attractive or repulsive energy (depending on the magnetic poles).
  • Electrical potential energy: This is the potential energy that is stored in two or more objects in an electric field. Objects with the same charges produce repulsive forces and objects with different charges have attractive forces.
  • Chemical potential energy: This is the potential energy that is stored in substances due to the position of their atoms. Examples include the fossil fuels and the food we eat.

Kinetic Energy

Kinetic energy is the energy possessed by an object due to its motion. Every moving object has kinetic energy. All the stars, planets, comets and other objects floating in space have kinetic energy. More precisely, kinetic energy is defined as the work that was needed to be done to accelerate a body of any mass from rest to its current velocity. In a vacuum, once a body has gained kinetic energy, it maintains this energy as long as its speed remains the same.

Mathematically, kinetic energy of a body in motion is expressed by the following equation:

KE = m.v2

Where, m is the mass of the body and v its current velocity.

Kinetic energy is expressed in Joules (kg.m-2.s-2). It is a scalar quantity and doesn’t have any direction. This means that it is described by its magnitude only.

Relationship between potential and kinetic energy

Potential energy is kinetic energy waiting to happen. In other words, potential energy stored in an object changes into kinetic energy when work is done on it. For example, when a rock sitting at the top of a cliff is pushed, it falls and its potential energy changes into kinetic energy.

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